Liquid crystal display device

ABSTRACT

To propose a liquid crystal display device for suppressing a wavelength dependence and a viewing dependence in a dark state. A polarizer ( 21   a ) of a circularly polarizer ( 21 ) and a polarizer ( 22   a ) of a circularly polarizer ( 22 ) are arranged such that an absorption axis (90°) of the polarizer ( 21   a ) and an absorption axis (0°) of the polarizer ( 22   a ) are at substantially right angle to each other. A retardation plate ( 21   b ) of a circularly polarizer ( 21 ) and a retardation plate ( 22   b ) of a circularly polarizer ( 22 ) are arranged such that a slow axis (165°) of the retardation plate ( 21   b ) and a slow axis (75°) of the retardation plate ( 22   b ) are at substantially right angle to each other. A retardation plate ( 21   c ) of a circularly polarizer ( 21 ) and a retardation plate ( 22   c ) of a circularly polarizer ( 22 ) are arranged such that a slow axis (105°) of the retardation plate ( 21   c ) and a slow axis (15°) of the retardation plate ( 22   c ) are at substantially right angle to each other.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display device,particularly to a liquid crystal display device for suppressingwavelength dependence and a viewing dependence in a dark state.

2. Description of Related Art

In a reflective liquid crystal display device, a circularly polarizer issometimes used to make a dark state (black display) excellent. In thereflective liquid crystal display device using the circularly polarizer,among incident light, either circularly polarized light of rightcircularly polarized light and left circularly polarized light isabsorbed, and only the other circularly polarized light is passedthrough the circularly polarizer. The circularly polarized light passedthrough the circularly polarizer varies the direction of circularpolarization when being reflected by a reflective plate. The circularlypolarized light with the varied direction cannot be passed through thecircularly polarizer and absorbed. As a result, it is possible to make adark state excellent (Japanese Laid-Open Patent Publication No.H06-11711 (paragraph [0050], FIG. 6)).

In applying the circular polarizer to a transflective liquid crystaldisplay device or transmissive liquid crystal display device, in orderto make a dark state excellent, it is required to arrange a pair ofcircularly polarizers on each outside of a liquid crystal cell so as tosandwich the liquid crystal cell. This is because it is intended inlight from the backlight in a transmissive mode that one circularlypolarizer absorbs either right circularly polarized light or leftcircularly polarized light, while the other circularly polarizer absorbsthe other circularly polarized light.

Thus, when circularly polarizers are used in a transflective liquidcrystal display device or transmissive liquid crystal display device, itis required to arrange a pair of circularly polarizers. However, underthe current circumstances, consideration is not given to a wavelengthdependence and a viewing dependence in a dark state of the circularlypolarizers.

SUMMARY OF THE INVENTION

In view of the foregoing, it is an object to provide a liquid crystaldisplay device capable of suppressing the wavelength dependence andviewing dependence in a dark state.

A liquid crystal display device of the present invention has a liquidcrystal cell having at least transmissive mode, and a pair of circularlypolarized light means having optical axes which are at substantiallyright angle to each other, and sandwiching the liquid crystal cell.

According to this arrangement, since the device is provided with a pairof circularly polarized light means having optical axes which are atsubstantially right angle to each other, the means mutually cancelsvariations in optical characteristics such as retardation. Therefore,the viewing dependence is suppressed, the wavelength dependence iscanceled thoroughly, and coloring in a dark state is thus eliminatedcompletely.

In the liquid crystal display device of the present invention, it ispreferable that the pair of circular polarized light means has a pair ofpolarizers, and a pair of retardation plates, which have optical axesthat are at substantially right angle to each other, arranged inside thepair of polarizers.

In the liquid crystal display device of the present invention, it ispreferable that the pair of circular polarized light means has aplurality of pairs of polarizers.

In the liquid crystal display device of the present invention, it ispreferable that the pair of retardation plates are uniaxial retardationplate or biaxial retardation plate. In addition, it is preferable thatthe biaxial retardation plate has Nz values in the range of 0 to 1.

In the liquid crystal display device of the present invention, it ispreferable that at least one of the pair of polarizers is a wide viewingangle polarizer.

In the liquid crystal display device of the present invention, it ispreferable that an optical axis of the retardation plate is a slow axis.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing an arrangement of a liquid crystaldisplay device according to Embodiments 1 to 4 of the present invention;

FIG. 2 is a view showing an arrangement of a circularly polarizeraccording to Embodiment 1 of the present invention;

FIG. 3 is a view showing a viewing dependence in a dark state in aliquid crystal display device according to Embodiment 1 of the presentinvention;

FIG. 4 is a view showing a wavelength dependence in a dark state in aliquid crystal display device according to Embodiments 1 to 4 of thepresent invention;

FIG. 5 is a view showing an arrangement of a circularly polarizer of aliquid crystal display device of a comparison example;

FIG. 6 is a view showing a viewing dependence in a dark state in aliquid crystal display device of comparison example;

FIG. 7 is a view showing a wavelength dependence in a dark state in aliquid crystal display device of a comparison example;

FIG. 8 is a view showing an arrangement of a circularly polarizeraccording to Embodiment 2 of the present invention;

FIG. 9 is a view showing a viewing dependence in a dark state in aliquid crystal display device according to Embodiment 2 of the presentinvention;

FIG. 10 is a view showing an arrangement of a circularly polarizeraccording to Embodiment 3 of the present invention;

FIG. 11 is a view showing a viewing dependence in a dark state in aliquid crystal display device according to Embodiment 3 of the presentinvention;

FIG. 12 is a view showing an arrangement of a circularly polarizeraccording to Embodiment 4 of the present invention; and

FIG. 13 is a view showing a viewing dependence in a dark state in aliquid crystal display device according to Embodiment 4 of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The subject matter of the present invention is to suppress a wavelengthdependence and a viewing dependence in a dark state in a liquid crystaldisplay device by comprising a liquid crystal cell having at leasttransmissive mode, and a pair of circularly polarized light means havingoptical axes which are at right angle to each other, and sandwiching theliquid crystal cell.

Embodiments of the present invention will be described specificallybelow with reference to accompanying drawings.

Embodiment 1

This Embodiment describes a case where a liquid crystal display deviceis a transflective liquid crystal display device, and a circularlypolarizer is comprised of a polarizer and two uniaxial retardationplates. FIG. 1 is a sectional view showing an arrangement of a liquidcrystal display device according to Embodiment 1 of the presentinvention.

In the liquid crystal display device as shown in FIG. 1, a transparentelectrode 13 is formed on one main surface of one glass substrate 11. Asmaterials for the transparent electrode 13, for example, there may beITO (Indium Tin Oxide), zinc oxide based material, titanium oxide basedmaterial, indium oxide-zinc oxide based material, Ga-added zinc oxidebased material, and p-type oxide material.

A resin layer 15 having transmissive regions patterned in pixels isformed on the transparent electrode 13. As materials for the resin layer15, general resist materials such as polyimide may be used. Further, areflective plate 17 is formed on the resin layer 15. As materials forthe reflective plate 17, aluminum and silver may be used. Each regionprovided with the reflective plate 17 is a reflective region, while eachregion without the reflective plate 17 is a transmissive region.

The patterning of the resin layer 15 and reflective plate 17 can becarried out as described below, for example. The resin layer is formedon the transparent electrode 13, and then, the reflective plate isformed on the resin layer. A resist layer is formed on the reflectiveplate, patterning is carried out by a photolithography method, and thereflective plate is etched using the patterned resist layer as a mask.Then, the resin layer is etched using the patterned reflective plate asa mask. In this way, the resin layer 15 and reflective plate 17 areformed. In addition, the case is described herein that after the resinlayer and reflective plate are laminated, the reflective plate and resinlayer are etched and patterned in this order. In the present invention,it may be possible that the reflective plate is laminated and undergoespatterning after the resin layer is laminated and undergoes patterning.

An alignment film 18 is formed on the reflective plate 17 and thetransparent electrode 13 in the transmissive region. As materials forthe alignment film 18, there may be resin materials such as polyimide.

A color filter 16 is formed on one main surface of the other glasssubstrate 12. A transparent electrode 14 is formed on the color filter16, and an alignment film 19 is formed on the transparent electrode 14.As respective materials for transparent electrode 14 and alignment film19, the same materials as those on the glass substrate 11 may be used.

In addition, transparent electrodes 13 and 14 respectively on glasssubstrates 11 and 12 compose a matrix of scanning electrode and signalelectrode, and enable display. In this way, pixels are formed on aliquid crystal panel 12 as in general liquid crystal panels. Further, asmethods of forming transparent electrodes 13 and 14, there may bemethods used in manufacturing general liquid crystal display devicessuch as a sputtering method, for example. As methods of formingalignment films 18 and 19, there may be methods used in manufacturinggeneral liquid crystal display devices such as a method including acoating process, drying process and rubbing process, for example.

A liquid crystal layer 20 is formed between the glass substrates 11 and12. The liquid crystal layer 20 is formed by arranging the glasssubstrates 11 and 12 with formed films such that the alignment films 18and 19 are opposed to each other, and filling a liquid crystal materialinto between the glass substrates 11 and 12. A circularly polarizer 21is disposed on the other main surface of the glass substrate 11, and acircularly polarizer 22 is disposed on the other main surface of theglass substrate 12.

FIG. 2 is a view showing an arrangement of the circularly polarizer ofthe liquid crystal display device according to Embodiment 1 of thepresent invention. In addition, in FIG. 2, in order to describe anarrangement of a pair of circularly polarizers, the liquid crystal cellis omitted which actually exists between the pair of circularlypolarizers. The circularly polarizer 21 is comprised of a polarizer 21 awith an absorption axis of 90°, a uniaxial retardation plate 21 b withretardation of 275 nm and a slow axis of 165°, and a uniaxialretardation plate 21 c with retardation of 137.5 nm and a slow axis of105°. The circularly polarizer 21 is obtained by arranging theretardation plate 21 c, retardation plate 21 b and polarizer 21 a on theglass substrate 11 in this order.

When two retardation plates are arranged between the polarizer andliquid crystal cell, it may be possible to paste one retardation plateto the polarizer and paste the other retardation plate to the liquidcrystal cell, to paste two retardation plates to the polarizersuccessively, or to paste two retardation plates to the liquid crystalcell successively.

The circularly polarizer 22 is comprised of a polarizer 22 a with anabsorption axis of 0° a uniaxial retardation plate 22 b with retardationof 275 nm and a slow axis of 75°, and a uniaxial retardation plate 22 cwith retardation of 137.5 nm and a slow axis of 15°. The circularlypolarizer 22 is obtained by arranging the retardation plate 22 c,retardation plate 22 b and polarizer 22 a on the glass substrate 12 inthis order. In addition, it is necessary that the circularlypolarization direction of the circularly polarizer 22 is inverse to thecircularly polarization direction of the circularly polarizer 21.

The polarizer 21 a of the circularly polarizer 21 and the polarizer 22 aof the circularly polarizer 22 are arranged such that the absorptionaxis (90°) of the polarizer 21 a and the absorption axis (0°) of thepolarizer 22 a are at substantially right angle to each other. Theretardation plate 21 b of the circularly polarizer 21 and theretardation plate 22 b of the circularly polarizer 22 are arranged suchthat the slow axis (165°) of the retardation plate 21 b and the slowaxis (75°) of the retardation plate 22 b are at substantially rightangle to each other. The retardation plate 21 c of the circularlypolarizer 21 and the retardation plate 22 c of the circularly polarizer22 are arranged such that the slow axis (105°) of the retardation plate21 c and the slow axis (15°) of the retardation plate 22 c are atsubstantially right angle to each other.

The operation of the liquid crystal display device with theaforementioned arrangement will be described below.

The case of reflective mode will be described first. In the reflectivemode, when external light is incident on a liquid crystal display device1, among the incident light, either circularly polarized light of rightcircularly polarized light and left circularly polarized light isabsorbed, and only the other circularly polarized light is passedthrough the polarizer 22. The circularly polarized light passed throughthe circularly polarizer 22 is reflected by the reflective plate 17 ofthe liquid crystal cell. At this point, the direction of circularlypolarization is varied. The circularly polarized light with the varieddirection cannot be passed through the circularly polarizer 22 andabsorbed in the circularly polarizer 22. As a result, it is possible tomake a dark state excellent.

In the transmissive mode, when light from the backlight (not shown) ispassed through the circularly polarizer 21, among the light, eitherright circularly polarized light or left circularly polarized light isabsorbed in the circularly polarizer 21. Since the circularlypolarization direction of the circularly polarizer 21 and the circularlypolarization direction of the circularly polarizer 22 are inverse toeach other, with respect to the light passed through the liquid crystalcell subsequently, the other circularly polarized light is absorbed inthe circularly polarizer 22. As a result, it is possible to make a darkstate excellent.

In the liquid crystal display device, since the device is provided witha pair of circularly polarizers having optical axes which are atsubstantially right angle to each other, in other words, since slow axesof retardation plates of the pair of circularly polarizers are atsubstantially right angle to each other, variations in retardation actto cancel each other. Therefore, it is possible to suppress thewavelength dependence and viewing dependence.

Examples will be described herein which were carried out to clarifyadvantages of the present invention.

The wavelength dependence and viewing dependence regarding thereflectivity were measured in the liquid crystal display device with thearrangement as shown in FIG. 2 provided with a pair of circularlypolarizers having optical axes that are at substantially right angle toeach other, and in a liquid crystal display device (comparison example)as shown in FIG. 5 provided with a pair of circularly polarizers havingoptical axes that are substantially parallel to each other. In addition,using a spectral luminance meter, the wavelength dependence was measuredin a darkroom with the spectral luminance meter arranged perpendicularlyto the panel of the liquid crystal cell, and using a luminance meter,the viewing dependence was measured in a darkroom while rotating abearing of the panel from 0° to 360° with the luminance meter fixed at60° to the perpendicular direction of the panel.

In the liquid crystal display device with the arrangement as shown inFIG. 2 according to this Embodiment, the viewing dependence is asindicted by a characteristic curve 31 as shown in FIG. 3, and thewavelength dependence is as indicted by a characteristic curve 32 asshown in FIG. 4. Further, in the liquid crystal display device of thecomparison example, the viewing dependence is as indicted by acharacteristic curve 33 as shown in FIG. 6, and the wavelengthdependence is as indicted by a characteristic curve 34 as shown in FIG.7.

In other words, in the arrangement according to this Embodiment, withrespect to the wavelength dependence, the slow axis of the retardationplate 21 b and the slow axis of the retardation plate 22 b are atsubstantially right angle to each other, and the slow axis of theretardation plate 21 c and the slow axis of the retardation plate 22 care at substantially right angle to each other, whereby wavelengthcharacteristics are mutually canceled. The state is thus substantiallythe same as a state where retardation plates are not present. Therefore,the wavelength dependency was canceled thoroughly, and coloring in adark state was completely eliminated.

Further, in the arrangement according to this Embodiment, with respectto the viewing dependence, the slow axis of the retardation plate 21 band the slow axis of the retardation plate 22 b are at substantiallyright angle to each other, and the slow axis of the retardation plate 21c and the slow axis of the retardation plate 22 c are at substantiallyright angle to each other, whereby viewing characteristics are mutuallycanceled. Therefore, the viewing dependence is suppressed more than inthe case of the liquid crystal display device of the comparison example.In addition, regarding the viewing dependence, when varying viewingdirections, the orthogonal relationship between the viewing directionand the direction of the panel plane deteriorates periodically, andtherefore, peaks and troughs appear periodically in the characteristiccurve 31 in FIG. 3. This phenomenon is considered to appear mainly dueto the polarizer.

Meanwhile, in the liquid crystal display device of the comparisonexample, as shown in FIG. 6, the viewing dependence is relatively large.Further, in the liquid crystal display device of the comparison example,as shown in FIG. 7, the wavelength dependence is large, and the panellooked colored in a dark state.

In this way, in the liquid crystal display device according to thisEmbodiment, the slow axis of the uniaxial retardation plate 21 b and theslow axis of the uniaxial retardation plate 22 b are at substantiallyright angle to each other, and the slow axis of the uniaxial retardationplate 21 c and the slow axis of the uniaxial retardation plate 22 c areat substantially right angle to each other, whereby the wavelengthdependency is canceled, and further, the viewing dependence issuppressed.

In addition, this Embodiment describes the case where the absorptionaxis of the polarizer 21 a and the absorption axis of the polarizer 22 aare at substantially right angle to each other. However, the presentinvention is applicable to the case where the absorption axis of thepolarizer 21 a and the absorption axis of the polarizer 22 a aresubstantially parallel to each other.

Embodiment 2

This Embodiment describes a case that a liquid crystal display device isa transflective liquid crystal display device, and a circularlypolarizer is comprised of a polarizer, a uniaxial retardation plate anda biaxial retardation plate.

FIG. 8 is a view showing an arrangement of a circularly polarizer of theliquid crystal display device according to Embodiment 2 of the presentinvention. A circularly polarizers 41 is comprised of a polarizer 41 awith an absorption axis of 90°, a biaxial retardation plate 41 b withretardation of 275 nm and a slow axis of 165°, and a uniaxialretardation plate 41 c with retardation of 137.5 nm and a slow axis of105°. The circularly polarizer 41 is obtained by arranging theretardation plate 41 c, retardation plate 41 b and polarizer 41 a on theglass substrate 11 in this order.

When two retardation plates are arranged between the polarizer andliquid crystal cell, it may be possible to paste one retardation plateto the polarizer and paste the other retardation plate to the liquidcrystal cell, to paste two retardation plates to the polarizersuccessively, or to paste two retardation plates to the liquid crystalcell successively.

A circularly polarizer 42 is comprised of a polarizer 42 a with anabsorption axis of 0°, a biaxial retardation plate 42 b with retardationof 275 nm and a slow axis of 75°, and a uniaxial retardation plate 42 cwith retardation of 137.5 nm and a slow axis of 15°. The circularlypolarizer 42 is obtained by arranging the retardation plate 42 c,retardation plate 42 b and polarizer 42 a on the glass substrate 12 inthis order. In addition, it is necessary that the circularlypolarization direction of the circularly polarizer 42 is inverse to thecircularly polarization direction of the circularly polarizer 41.

The polarizer 41 a of the circularly polarizer 41 and the polarizer 42 aof the circularly polarizer 42 are arranged such that the absorptionaxis (90°) of the polarizer 41 a and the absorption axis (0°) of thepolarizer 42 a are at substantially right angle to each other. Theretardation plate 41 b of the circularly polarizer 41 and theretardation plate 42 b of the circularly polarizer 42 are arranged suchthat the slow axis (165°) of the retardation plate 41 b and the slowaxis (75°) of the retardation plate 42 b are at substantially rightangle to each other. The retardation plate 41 c of the circularlypolarizer 41 and the retardation plate 42 c of the circularly polarizer42 are arranged such that the slow axis (105°) of the retardation plate41 c and the slow axis (15°) of the retardation plate 42 c are atsubstantially right angle to each other.

The operation of the liquid crystal display device with theaforementioned arrangement is the same as in Embodiment 1.

In the liquid crystal display device, since the device is provided witha pair of circularly polarizers having optical axes which are atsubstantially right angle to each other, in other words, since slow axesof retardation plates of the pair of circularly polarizers are atsubstantially right angle to each other, variations in retardation actto cancel each other. Therefore, it is possible to suppress thewavelength dependence and viewing dependence.

In the liquid crystal display device according to this Embodiment, sincethe circularly polarizer has a biaxial retardation plate, such a statearises that there are no variations in retardation characteristics. Thisrespect is described in SID 92 DIGEST, pages 397 to 400, Y. Fujimura etal, “Optical Properties of Retardation Film”. Therefore, the viewingdependency is further suppressed. In addition, the Nz value (valuerepresenting a biaxial rate) of the biaxial retardation plate ispreferably in the range of 0 to 1 where the viewing dependence of theretardation plate becomes small, and the most preferably, is 0.5.

Examples will be described herein which were carried out to clarifyadvantages of the present invention.

The wavelength dependence and viewing dependence regarding thereflectivity ware measured in the liquid crystal display device with thearrangement as shown in FIG. 8 provided with a pair of circularlypolarizers having optical axes that are at substantially right angle toeach other. In addition, using a spectral luminance meter, thewavelength dependence was measured in a darkroom with the spectralluminance meter arranged perpendicularly to the panel, and using aluminance meter, the viewing dependence was measured in a darkroom whilerotating a bearing of the panel from 0° to 360° with the luminance meterfixed at 60° to the perpendicular direction of the panel.

In the liquid crystal display device with the arrangement as shown inFIG. 8 according to this Embodiment, the viewing dependence is asindicted by a characteristic curve 35 as shown in FIG. 9. With respectto the viewing dependence, the slow axis of the retardation plate 41 band the slow axis of the retardation plate 42 b are at substantiallyright angle to each other, and the slow axis of the retardation plate 41c and the slow axis of the retardation plate 42 c are at substantiallyright angle to each other, whereby viewing characteristics are mutuallycanceled. Therefore, the viewing dependence is suppressed. Further,since the biaxial retardation plate is used, the viewing dependence wassuppressed more than in Embodiment 1.

Further, in the arrangement according to this Embodiment, with respectto the wavelength dependency, as in Embodiment 1, the wavelengthdependency was canceled thoroughly, and coloring in a dark state wascompletely eliminated.

Thus, in the liquid crystal display device in this Embodiment, the slowaxis of the biaxial retardation plate 41 b and the slow axis of thebiaxial retardation plate 42 b are at substantially right angle to eachother, and the slow axis of the uniaxial retardation plate 41 c and theslow axis of the uniaxial retardation plate 42 c are at substantiallyright angle to each other, whereby the wavelength dependence iscanceled, and the viewing dependence is more suppressed.

In addition, this Embodiment describes the case where the absorptionaxis of the polarizer 41 a and the absorption axis of the polarizer 42 aare at substantially right angle to each other. However, the presentinvention is applicable to the case where the absorption axis of thepolarizer 41 a and the absorption axis of the polarizer 42 a aresubstantially parallel to each other.

Embodiment 3

This Embodiment describes a case that a liquid crystal display device isa transflective liquid crystal display device, and a circularlypolarizer is comprised of a polarizer, and two biaxial retardationplates.

FIG. 10 is a view showing an arrangement of the circularly polarizer ofthe liquid crystal display device according to Embodiment 3 of thepresent invention. A circularly polarizers 51 is comprised of apolarizer 51 a with an absorption axis of 90°, a biaxial retardationplate 51 b with retardation of 275 nm and a slow axis of 165°, and abiaxial retardation plate 51 c with retardation of 137.5 nm and a slowaxis of 105°. The circularly polarizer 51 is obtained by arranging theretardation plate 51 c, retardation plate 51 b and polarizer 51 a on theglass substrate 11 in this order.

When two retardation plates are arranged between the polarizer andliquid crystal cell, it may be possible to paste one retardation plateto the polarizer and paste the other retardation plate to the liquidcrystal cell, to paste two retardation plates to the polarizersuccessively, or to paste two retardation plates to the liquid crystalcell successively.

A circularly polarizer 52 is comprised of a polarizer 52 a with anabsorption axis of 0°, a biaxial retardation plate 52 b with retardationof 275 nm and a slow axis of 75°, and a biaxial retardation plate 52 cwith retardation of 137.5 nm and a slow axis of 15°. The circularlypolarizer 52 is obtained by arranging the retardation plate 52 c,retardation plate 52 b and polarizer 52 a on the glass substrate 12 inthis order. In addition, it is necessary that the circularlypolarization direction of the circularly polarizer 52 is inverse to thecircularly polarization direction of the circularly polarizer 51.

The polarizer 51 a of the circularly polarizer 51 and the polarizer 52 aof the circularly polarizer 52 are arranged such that the absorptionaxis (90°) of the polarizer 51 a and the absorption axis (0°) of thepolarizer 52 a are at substantially right angle to each other. Theretardation plate 51 b of the circularly polarizer 51 and theretardation plate 52 b of the circularly polarizer 52 are arranged suchthat the slow axis (165°) of the retardation plate 51 b and theslow-axis (75°) of the retardation plate 52 b are at substantially rightangle to each other. The retardation plate 51 c of the circularlypolarizer 51 and the retardation plate 52 c of the circularly polarizer52 are arranged such that the slow axis (105°) of the retardation plate51 c and the slow axis (15°) of the retardation plate 52 c are atsubstantially right angle to each other.

The operation of the liquid crystal display device with theaforementioned arrangement is the same as in Embodiment 1.

In the liquid crystal display device, since the device is provided witha pair of circularly polarizers having optical axes which are atsubstantially right angle to each other, in other words, since slow axesof retardation plates of the pair of circularly polarizers are atsubstantially right angle to each other, variations in retardation actto cancel each other. Therefore, it is possible to suppress thewavelength dependence and viewing dependence.

In the liquid crystal display device according to this Embodiment, sincethe circularly polarizer has two biaxial retardation plates, such astate arises that there are no variations in retardationcharacteristics. This respect is described in SID 92 DIGEST, pages 397to 400, Y. Fujimura et al, “Optical Properties of Retardation Film”.Therefore, the viewing dependency is further suppressed than inEmbodiment 2. In addition, the Nz value (value representing a biaxialrate) of the biaxial retardation plate is preferably in the range of 0to 1 where the viewing dependence of the retardation plate becomessmall, and the most preferably, is 0.5.

Examples will be described herein which were carried out to clarifyadvantages of the present invention.

The wavelength dependence and viewing dependence regarding thereflectivity were measured in the liquid crystal display device with thearrangement as shown in FIG. 10 provided with a pair of circularlypolarizers having optical axes that are at substantially right angle toeach other. In addition, using a spectral luminance meter, thewavelength dependence was measured in a darkroom with the spectralluminance meter arranged perpendicularly to the panel, and using aluminance meter, the viewing dependence was measured in a darkroom whilerotating a bearing of the panel from 0° to 360° with the luminance meterfixed at 60° to the perpendicular direction of the panel.

In the liquid crystal display device with the arrangement as shown inFIG. 10 according to this Embodiment, the viewing dependence is asindicted by a characteristic curve 36 as shown in FIG. 11. With respectto the viewing dependence, the slow axis of the retardation plate 51 band the slow axis of the retardation plate 52 b are at substantiallyright angle to each other, and the slow axis of the retardation plate 51c and the slow axis of the retardation plate 52 c are at substantiallyright angle to each other, whereby viewing characteristics are mutuallycanceled. Therefore, the viewing dependence is suppressed. Further,since two biaxial retardation plates are used, the viewing dependencewas suppressed more than in Embodiment 1.

Further, in the arrangement according to this Embodiment, with respectto the wavelength dependency, as in Embodiment 1, the wavelengthdependency was canceled thoroughly, and coloring in a dark state wascompletely eliminated.

Thus, in the liquid crystal display device in this Embodiment, the slowaxis of the biaxial retardation plate 51 b and the slow axis of thebiaxial retardation plate 52 b are at substantially right angle to eachother, and the slow axis of the biaxial retardation plate 51 c and theslow axis of the biaxial retardation plate 52 c are at substantiallyright angle to each other, whereby the wavelength dependence iscanceled, and the viewing dependence is more suppressed.

In addition, this Embodiment describes the case where the absorptionaxis of the polarizer 51 a and the absorption axis of the polarizer 52 aare at substantially right angle to each other. However, the presentinvention is applicable to the case where the absorption axis of thepolarizer 51 a and the absorption axis of the polarizer 52 a aresubstantially parallel to each other.

Embodiment 4

This Embodiment describes a case that a liquid crystal display device isa transflective liquid crystal display device, and a circularlypolarizer is comprised of a wide viewing angle polarizer, and twobiaxial retardation plates.

FIG. 12 is a view showing an arrangement of the circularly polarizer ofthe liquid crystal display device according to Embodiment 4 of thepresent invention. A circularly polarizers 61 is comprised of a wideviewing angle polarizer 61 a with an absorption axis of 90°, a biaxialretardation plate 61 b with retardation of 275 nm and a slow axis of165°, and a biaxial retardation plate 61 c with retardation of 137.5 nmand a slow axis of 105°. The circularly polarizer 61 is obtained byarranging the retardation plate 61 c, retardation plate 61 b and wideviewing angle polarizer 61 a on the glass substrate 11 in this order.

When two retardation plates are arranged between the wide viewing anglepolarizer and liquid crystal cell, it may be possible to paste oneretardation plate to the wide viewing angle polarizer and paste theother retardation plate to the liquid crystal cell, to paste tworetardation plates to the wide viewing angle polarizer successively, orto paste two retardation plates to the liquid crystal cell successively.

A circularly polarizer 62 is comprised of a wide viewing angle polarizer62 a with an absorption axis of 0°, a biaxial retardation plate 62 bwith retardation of 275 nm and a slow axis of 75°, and a biaxialretardation plate 62 c with retardation of 137.5 nm and a slow axis of15°. The circularly polarizer 62 is obtained by arranging theretardation plate 62 c, retardation plate 62 b and wide viewing anglepolarizer 62 a on the glass substrate 12 in this order. In addition, itis necessary that the circularly polarization direction of thecircularly polarizer 62 is inverse to the circularly polarizationdirection of the circularly polarizer 61.

The wide viewing angle polarizer 61 a of the circularly polarizer 61 andthe wide viewing angle polarizer 62 a of the circularly polarizer 62 arearranged such that the absorption axis (90°) of the wide viewing anglepolarizer 61 a and the absorption axis (0°) of the wide viewing anglepolarizer 62 a are at substantially right angle to each other. Theretardation plate 61 b of the circularly polarizer 61 and theretardation plate 62 b of the circularly polarizer 62 are arranged suchthat the slow axis (165°) of the retardation plate 61 b and the slowaxis (75°) of the retardation plate 62 b are at substantially rightangle to each other. The retardation plate 61 c of the circularlypolarizer 61 and the retardation plate 62 c of the circularly polarizer62 are arranged such that the slow axis (105°) of the retardation plate61 c and the slow axis (15°) of the retardation plate 62 c are atsubstantially right angle to each other.

The operation of the liquid crystal display device with theaforementioned arrangement is the same as in Embodiment 1.

In the liquid crystal display device, since the device is provided witha pair of circularly polarizers having optical axes which are atsubstantially right angle to each other, in other words, since slow axesof retardation plates of the pair of circularly polarizers are atsubstantially right angle to each other, variations in retardation actto cancel each other. Therefore, it is possible to suppress thewavelength dependence and viewing dependence.

In the liquid crystal display device according to this Embodiment, sincethe circularly polarizer has two biaxial retardation plates, such astate arises that there are no variations in retardationcharacteristics. This respect is described in SID 92 DIGEST, pages 397to 400, Y. Fujimura et al, “Optical Properties of Retardation Film”.Therefore, the viewing dependency is further suppressed than inEmbodiment 2. In addition, the Nz value (value representing a biaxialrate) of the biaxial retardation plate is preferably in the range of 0to 1 where the viewing dependence of the retardation plate becomessmall, and the most preferably, is 0.5.

Further, the liquid crystal display device according to this Embodimentuses a wide viewing angle polarizer and biaxial retardant plates, andthereby is capable of reducing the viewing dependence further. Thisrespect is described in Asia Display/IDW'01, pages 485 to 488, T.Ishinabe et al “A Wide Viewing Angle Polarizer and a Quarter-wave platewith a Wide Wavelength Range for Extremely High Quality LCDs”.

Examples will be described herein which were carried out to clarifyadvantages of the present invention.

The wavelength dependence and viewing dependence regarding thereflectivity were measured in the liquid crystal display device with thearrangement as shown in FIG. 12 provided with a pair of circularlypolarizers having optical axes that are at substantially right angle toeach other. In addition, using a spectral luminance meter, thewavelength dependence was measured in a darkroom with the spectralluminance meter arranged perpendicularly to the panel, and using aluminance meter, the viewing dependence was measured in a darkroom whilerotating a bearing of the panel from 0° to 360° with the luminance meterfixed at 60° to the perpendicular direction of the panel.

In the liquid crystal display device with the arrangement as shown inFIG. 12 according to this Embodiment, the viewing dependence is asindicted by a characteristic curve 37 as shown in FIG. 13. With respectto the viewing dependence, the slow axis of the retardation plate 61 band the slow axis of the retardation plate 62 b are at substantiallyright angle to each other, and the slow axis of the retardation plate 61c and the slow axis of the retardation plate 62 c are at substantiallyright angle to each other, whereby viewing characteristics are mutuallycanceled. Therefore, the viewing dependence is suppressed. Further,since a wide viewing angle polarizer and two biaxial retardation platesare used, the viewing dependence was suppressed completely.

Further, in the arrangement according to this Embodiment, with respectto the wavelength dependency, as in Embodiment 1, the wavelengthdependency was canceled thoroughly, and coloring in a dark sate wascompletely eliminated.

Thus, in the liquid crystal display device in this Embodiment, the slowaxis of the biaxial retardation plate 61 b and the slow axis of thebiaxial retardation plate 62 b are at substantially right angle to eachother, the slow axis of the biaxial retardation plate 61 c and the slowaxis of the biaxial retardation plate 62 c are at substantially rightangle to each other, and further, a wide viewing angle polarizer isused, whereby the wavelength dependence is canceled, and the viewingdependence is canceled also.

In addition, this Embodiment describes the case where the absorptionaxis of the wide viewing angle polarizer 61 a and the absorption axis ofthe wide viewing angle polarizer 62 a are at substantially right angleto each other. However, the present invention is applicable to the casewhere the absorption axis of the wide viewing angle polarizer 61 a andthe absorption axis of the wide viewing angle polarizer 62 a aresubstantially parallel to each other.

The present invention is not limited to aforementioned Embodiments 1 to4, and is capable of being carried into practice with variousmodifications thereof. For example, while Embodiments 1 to 4 describethe case where a liquid crystal display device is a transflective liquidcrystal display device, the present invention is similarly applicable toa transmissive liquid crystal display device. Further, while Embodiments1 to 4 describe the case where a passive liquid crystal display elementis used as a liquid crystal cell, the present invention allows the useof active matrix liquid crystal display element.

Values in polarizers and retardation plates in Embodiments 1 to 4 arenot limited to the values in the aforementioned Embodiments. In otherwords, these values are relative values between a pair of circularlypolarizers, and therefore, are capable of being varied as appropriate,as long as the relative relationship between the pair of circularlypolarizers is maintained. For example, it may be possible that a slowaxis of one polarizer is a, while a slow axis of the other polarizer isα′=α±90±15. Meanwhile, it may be possible that an absorption axis of oneretardation plate is β, while an absorption axis of the otherretardation plate is β′=β±90±15. Further, as a retardation plate, it maybe possible to use a ½-wavelength plate with a retardation value of 200to 400 nm, or a ¼-wavelength plate with a retardation value of 50 to 250nm.

The present invention is applicable to all the liquid crystal displaydevices used in cellular telephones and PDAs (Personal DigitalAssistants) and to liquid crystal display devices for automobiles andaircraft.

As described above, since the liquid crystal display device of thepresent invention is provided with a pair of circularly polarized lightmeans having optical axes which are at substantially right angle to eachother, variations in optical characteristics such as retardation arecanceled mutually. Therefore, the viewing dependence is suppressed, thewavelength dependence is canceled thoroughly, and coloring in a darkstate is completely eliminated.

This application is based on the Japanese Patent Application No2002-361294 filed on Dec. 12, 2002, entire content of which is expresslyincorporated by reference herein.

1. A liquid crystal display device comprising: a liquid crystal cellhaving at least transmissive mode; and a pair of circularly polarizedlight means having optical axes which are at substantially right angleto each other, and sandwiching said liquid crystal cell.
 2. The deviceaccording to claim 1, wherein said a pair of circular polarized lightmeans comprises a pair of polarizers, and a pair of retardation plates,which are at substantially right angle to each other, arranged insidesaid a pair of polarizers.
 3. The device according to claim 2, whereinsaid a pair of circular polarized light means has a plurality of pairsof polarizers.
 4. The device according to claim 1, wherein said a pairof retardation plates are uniaxial retardation plate or biaxialretardation plate.
 5. The device according to claim 4, wherein saidbiaxial retardation plate has Nz values in the range of 0 to
 1. 6. Thedevice according to claim 1, wherein at least one of said a pair ofpolarizers is a wide viewing angle polarizer.
 7. The device according toclaim 1, wherein an optical axis of said retardation plate is a slowaxis.
 8. The device according to claim 1, wherein said liquid crystaldisplay device is a transflective liquid crystal display device or atransmissive liquid crystal display device.